1. Technical Field
The present invention relates generally to balloon angioplasty. In particular, the present invention relates to an improved catheter apparatus and method for thermal balloon angioplasty treatment of a blood vessel stenosis.
2. Description of the Prior Art
It is known that restricted blood flow through a blood vessel stenosis is treatable by balloon angioplasty. However, it is also known that after such balloon angioplasty treatment certain undesirable conditions, such as abrupt reclosure or restenosis, can occur. Improvements to balloon angioplasty and blood vessel stenosis treatment are disclosed in U.S. Pat. Nos. 4,799,479 and 5,190,540 in order to minimize the occurrence of the undesirable conditions of reclosure and restenosis.
U.S. Pat. No. 4,799,479 discloses inflating a balloon in a blood vessel treatment region against a stenosis. During the time that the balloon is inflated to expand and open the stenosis, heat is applied to the fluid which has inflated the balloon. The fractured stenosis plaque and the blood vessel expanded tissue which result from inflation of the balloon are elevated in temperature to fuse together the fragmented segments of the stenosis and to treat the expanded tissue. This elevation in temperature also coagulates any blood trapped between the fragmented segments or between the fragmented segments of the stenosis and the expanded tissue of the blood vessel created by the expansion and deformation of the treatment region of the blood vessel. The heating of the balloon inflating fluid is performed after the balloon is inflated and takes some amount of time.
U.S. Pat. No. 5,190,540 discloses an improved apparatus and method for thermal balloon angioplasty. The apparatus includes a balloon attached to a distal end of a catheter body. The catheter body has two fluid passages extending therethrough. One passage directs fluid into the balloon and the other passage directs fluid away from the balloon. Each passage has an opening communicating with one end of the balloon.
The method disclosed in the '540 patent includes heating the balloon inflating fluid prior to balloon inflation. This causes the fatty or lipid tissue in the stenosis treatment region of the blood vessel to liquify and become relatively pliable. Thus, as the balloon is inflated any fractures to the stenosis plaque and any fissures or mechanical trauma to the blood vessel wall are minimized due to the relatively pliable condition of the stenosis and surrounding tissue in the treatment region of the blood vessel. After the heated and inflated balloon is maintained in contact with the treatment region for a predetermined time interval, the fluid inflating the balloon is cooled.
The cooling is accomplished while the balloon is inflated by displacing the heated fluid in the balloon with a fluid at a relatively lower temperature. The cooling action of the balloon re-establishes the solid form of the tissue located in the treatment region of the blood vessel. Injecting cool fluid into the balloon causes the heat softened and pliable tissue to congeal in the shape of the inflated balloon. This minimizes tissue elastic recoil and tissue thermal injury which may cause abrupt vessel closure and restenosis. Heat is applied for only a short term and the blood vessel is remolded to increase the likelihood it remains opened.
It is desirable to minimize the total treatment time that the balloon is inflated to avoid long periods of little or no blood flow. However, the heat treatment and the cooling treatment time intervals are relatively fixed. It is important to minimize the transition time between a heat treatment cycle and/or cooling treatment cycle.